Altman, Sidney (1939-), a Canadian-born American molecular biologist, transformed scientific thought about how living cells work and how life began millions of years ago. Altman shared the Nobel Prize in chemistry in 1989 for his discovery that ribonucleic acid (RNA) could act as a catalyst to accelerate chemical reactions. Before Altman's findings, biologists had believed that only enzymes, which are a type of protein, could perform this role.

Altman's experiments focused on the function RNA plays in cellular reactions. Deoxyribonucleic acid (DNA), provides genetic information vital to enzyme production. RNA copies this information and transfers it to enzymes. In turn, enzymes, which act as catalysts, are essential for RNA and DNA processes. Altman's work revealed that unlike other enzymes, the enzyme ribonuclease P (RNase P), had both a protein strand and an RNA strand. Further testing showed that the RNA strand in RNase P could act as a catalyst on its own. Altman's work demonstrated that RNA might have been the earliest catalyst of primitive cellular processes. In independent experiments, Thomas Robert Cech, who shared the 1989 Nobel Prize in chemistry with Altman, verified the catalytic properties of RNA.

Altman graduated in 1960 from the Massachusetts Institute of Technology and received a Ph.D. degree in molecular biology from the University of Colorado. In 1969, he obtained a fellowship to work at the Medical Research Council Molecular Biology Laboratory in Cambridge, England, where he began the experiments that would lead to his groundbreaking RNA discoveries. In 1971, Altman accepted a faculty job at Yale University. He served as dean of Yale College, the undergraduate school at Yale, from 1985 to 1989.

In addition to winning the Nobel Prize in chemistry in 1989, Altman also received the Rosentiel Award for Basic Biomedical Research that year. He is a member of the National Academy of Sciences.

Altman and his wife, Ann Korner, have two children.